1. Field of the Invention
This invention relates to sheet lifters which are used to facilitate the closing of loose leaf binders such that the pages which are secured in the loose leaf will not bind and tear when the loose leaf is closed.
2. The Prior Art
Loose leaf binders have long been used as a practical and convenient means of securing individual pages or sheets of paper in a convenient fashion so that the pages can be removed or replaced from time to time. It is not uncommon when using loose leaf binders that when the outer leaves of the binder are closed the pages or sheets are caught between the rings of the binder and the outer leaves thus making it difficult to close the loose leaf and sometimes tearing the outermost pages.
There have been several attempts in the prior art to solve this problem. Typically, sheet lifters are secured to the rings of the binder such that the pages or sheets are supported by the sheet lifters at each of the rings. The function of the sheet lifters is to help move the sheets upward along the rings when the covers of the binder are closed, thus helping to prevent the sheets from being caught between the rings and the outer leaves of the loose leaf when the leaves are folded together so as to close the loose leaf.
One of the most common types of prior art leaf lifter devices is illustrated in FIG. 1 and is disclosed in U.S. Pat. No. 3,591,300. The loose leaf binder generally designated at 14 includes a backing or spine 15 to which two cover leaves 16 and 17 are hinged as at 18 and 19. The loose leaf binder includes a plurality of rings generally designated 12, of which only one is shown in FIG. 1. Each ring comprises two arcuate segments 12a and 12b which mate at the uppermost ends thereof when in the closed position. The lower ends of the arcuate ring segments 12a and 12b are connected to a spring mechanism (not shown) to provide the conventional snap-action which is used to open or close the rings when it is desired to insert or remove pages. The spring mechanism is housed by a longitudinal cover plate 20 securely attached to the inside surface of the spine 15.
The prior art type leaf lifter of this device is typically constructed of molded plastic. The device includes two parts generally designated at 26 and 28 which are of identical construction and which are joined by an integral connection 29. The two sheet lifter parts 26 and 28 each include a flat body portion 30 which includes an upwardly inclined portion 32 which is connected at a score line or groove 52 to the connector 29. Formed on the body portion 30 are narrow tracks 42 and 43 which are inclined at the end where the sheet lifter parts 26 and 28 are joined to the connector 29.
In its operation, as the outer leaves 16 and 17 of the loose leaf are closed sheet lifter parts 26 and 28 help raise the pages along the rings 12 in order to prevent them from binding.
While in many respects this type of prior art leaf lifter works well, it also suffers from certain disadvantages. For example, one of the problems with this type of leaf lifter is that sheet lifter parts 26 and 28 can themselves at times bind so that they do not slide freely along the rings 12 thus making it difficult to close the loose leaf. Also, the connector portion 29 is relatively cumbersome and tends to take up unnecessary space, both in the open and closed positions of the loose leaf. Another disadvantage with this type of prior art leaf lifter is that when the outer leaves 16 and 17 are folded, the outermost edges 34 of the sheet lifter parts 26 and 28 are lifted first. This necessitates that the sheet lifter parts 26 and 28 be inclined as at tracks 42 and 43 in order to also lift the pages and prevent them from binding, which even then is not always successful.
Other similar types of prior art leaf lifter devices have been known and described in the prior art. See, for example, U.S. Pat. Nos. 3,306,301, 2,276,987, 2,179,986, 2,179,757, and 2,035,284. While the various leaf lifter devices mentioned in these patents are all somewhat different from one another, they are similar to the leaf lifter device illustrated in FIG. 1 in that they are typically secured about the rings of the loose leaf binder and they necessitate that the outer edges of the sheet lifter be lifted as the outer leaves of the loose leaf are closed. Thus, these prior art type leaf lifters suffer from many of the same or similar disadvantages as those mentioned above in connection with the device illustrated in FIG. 1.